Measurement of electrolytes, proteins, nonprotein nitrogen compounds, sugars, lipids, enzymes, and the like in blood is called clinical chemistry examination, which is an important test for diagnosis, treatment, and prevention of a disease. Quite a many substances other than target substances to be measured exist in blood used as a test sample and often interfere with measurement of a target substance. Therefore, techniques are adopted in which a specimen is treated with an agent for avoiding the interference before measuring the target substance. At this time, collected whole blood is usually centrifuged or the like to obtain plasma or serum beforehand. This is because, when blood component analysis using whole blood as a sample that requires elimination or conversion of components interfering with the measurement is performed, cell components such as blood cells may affect the measurement, isolation of blood cells may be difficult due to hemolysis, hemoglobin having a peroxidase activity, which abundantly exists in blood cells, may interfere with the measurement, and the like.
In recent years, the number of diabetic patients has been increasing as the diet has become richer. To prevent complications in diabetic patients, blood sugar levels need to be maintained at the levels close to those of healthy individuals, and apparatuses for self-measurement of blood sugar levels are widely used so that patients can monitor the blood sugar levels themselves at home. However, since blood sugar levels vary depending on the meal, and the measurement has to be done frequently, patients suffer heavy burdens. It is also difficult for patients to interpret measured values due to lack of knowledge.
Meanwhile, 1,5-anhydroglucitol is an excellent marker for checking a blood sugar control condition in diabetic patients over the past one week without being affected by meals, and development of a self-measurement kit using 1,5-anhydroglucitol, which can accurately check a blood sugar control condition at home by once-weekly measurement alone, will be of a great advantage for patients. Furthermore, it would also be useful in mass screening. However, since the concentration of 1,5-anhydroglucitol in blood is extremely low compared with the blood sugar level, and blood sugar, i.e., glucose interferes with measurement of 1,5-anhydroglucitol, development of self-measurement kits including those using a trace amount of whole blood as a sample as it is has not been realized.
Furthermore, glucose exists at a high concentration in the intracellular fluid in a blood cell and is balanced with glucose in the extracellular fluid across the cell membrane. If glucose in the extracellular fluid is converted to a substance that does not interfere with measurement, glucose in the intracellular fluid in the blood cell is released through the cell membrane and interferes with the measurement.
Examples of the blood component analysis requiring elimination or conversion of components that interfere with measurement include those described in the following publications. In Patent Document 1, blood cells are isolated from whole blood, and then ascorbic acid, a component interfering with measurement, is eliminated by ascorbic acid oxidase to measure creatinine.
In Patent Documents 2, 3, and 4, not whole blood but serum is used as a specimen to measure sorbitol in Patent Document 2, mannose in Patent Document 3, and myoinositol in Patent Document 4. In any case, glucose, a component interfering with measurement, is eliminated or converted in pretreatment.
When 1,5-anhydroglucitol is to be measured, not whole blood but serum is used as a specimen as described in Patent Documents 5, 6, 7, 8, and the like. Glucose is oxidized by glucose oxidase or also phosphorylated by hexokinase or glucokinase in Patent Document 5, is oxidized by glucose oxidase or glucose dehydrogenase in Patent Document 6, and is converted to fructose-1,6-diphosphate by hexokinase, phosphohexose isomerase, and 6-phosphofructokinase or glucose isomerase, fructokinase, and 6-phosphofructokinase in Patent Documents 7 and 8, and then 1,5-anhydroglucitol is measured. It is noted that glucose is converted to glucono-1,5-lactone, glucose-6-phosphate, gluconic acid, fructose-6-phosphate, fructose, or the like in these publications.
In these measurements of blood components, whole blood is not directly used as a sample, and use of a centrifuge and a large amount of blood are required to isolate blood cells, with many process steps of treatment.
Furthermore, a device to which a member is connected by external manipulation is described in Patent Document 1.    Patent Document 1: JP-B-07-36756    Patent Document 2: JP-A-08-298996    Patent Document 3: JP-A-2001-197900    Patent Document 4: JP-A-2001-190299    Patent Document 5: Japanese Patent No. 2983015    Patent Document 6: JP-A-2001-78797    Patent Document 7: Japanese Patent No. 3170320    Patent Document 8: Japanese Patent No. 3217180